We describe a new method for determining component values and transistor
dimensions for CMOS operational amplifiers (op-amps). We observe that a wide
variety of design objectives and constraints have a special form, i.e., they
are posynomial functions of the design variables. As a result the amplifier
design problem can be expressed as a special form of optimization problem
called geometric programming, for which very efficient global optimization
methods have been developed. As a consequence we can efficiently determine
globally optimal amplifier designs, or globally optimal trade-offs among
competing performance measures such as power, open-loop gain, and bandwidth.
Our method therefore yields completely automated synthesis of (globally)
optimal CMOS amplifiers, directly from specifications. In this paper we apply
this method to a specific, widely used operational amplifier architecture,
showing in detail how to formulate the design problem as a geometric program.
We compute globally optimal trade-off curves relating performance measures such
as power dissipation, unity-gain bandwidth, and open-loop gain. We show how the
method can be used to synthesize robust designs, i.e., designs guaranteed to
meet the specifications for a variety of process conditions and parameters.